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Abstract
Circumbinary planetary systems recently discovered by Kepler represent an important
testbed for planet formation theories. Planetesimal growth in disks around binaries
has been expected to be inhibited interior to ~10 AU by secular excitation of high
relative velocities between planetesimals, leading to their collisional destruction
(rather than agglomeration). Here we show that gravity of the gaseous circumbinary
disk in which planets form drives fast precession of both the planetesimal and binary
orbits, resulting in strong suppression of planetesimal eccentricities beyond 2-3
AU and making possible growth of 1-100 km objects in this region. The precise location
of the boundary of accretion-friendly region depends on the size of the inner disk
cavity cleared by the binary torques and on the disk mass (even 0.01 M_Sun disk strongly
suppresses planetesimal excitation), among other things. Precession of the orbit of
the central binary, enhanced by the mass concentration naturally present at the inner
edge of a circumbinary disk, plays key role in this suppression, which is a feature
specific to the circumbinary planet formation.